Supermarket refrigeration has traditionally been accomplished via centralized parallel compressor systems with long liquid and suction branches piped to and from the evaporators in the refrigerated display cases. One example of a refrigeration system including a parallel compressor system is described in U.S. Patent Application Publication No. 2002/0020175, published Feb. 21, 2002, the content of which is incorporated herein by reference. The parallel compressor configuration allows for stepwise capacity modulation via compressor cycling. One typical disadvantage with these systems is that the compressors generate large amounts of acoustic noise. Remotely locating elements (e.g., compressors, condensers) of the system solves the problem of acoustic noise in the retail sales area. However, the remote location results in expensive field piping, large refrigerant charge and leakage, and parasitic heating of the liquid and suction piping.
An alternative to the large, centralized parallel rack refrigeration system is a system used by supermarkets typically referred to as a distributed refrigeration system. An example of a distributed refrigeration system is disclosed in U.S. Pat. No. 5,440,894, issued Aug. 15, 1995, the content of which is incorporated herein by reference. The distributed system is intended for cooling a plurality of fixtures in multiple cooling zones within a shopping area of a food store. The system comprises a condensing unit rack configured to accommodate the maximum refrigeration loads of the associated zones and being constructed to support the components of a closed refrigeration circuit including a plurality of multiplexed compressors and associated high side and low side refrigerant delivery. The system also comprises a suction header extending from the rack and being operatively connected to one or more evaporators. The system also has a condenser with a cooling source remote from the compressor rack but operatively configured to provide a heat exchange relationship. While the distributed refrigeration system is typically closer to the loads (e.g., the merchandisers) as compared to the centralized system, the remote location of the components of the distributed system results in increased field piping, excess refrigerant charge and leakage, and some parasitic heating.
Another alternative to the above systems includes a self-contained, refrigeration display merchandiser comprising multiple horizontal scroll compressors. One example of such a merchandiser is described in U.S. Pat. No. 6,381,972 B1, issued May 7, 2002, the content of which is incorporated herein by reference. The self-contained merchandiser comprising multiple horizontal scroll compressors are relatively quiet when mounted in an insulated box, but lack an efficient low-cost capacity modulation scheme.
A yet another alternative to the above systems include a self-contained, refrigerated display merchandiser having a single reciprocating compressor. The self-contained, refrigerated display case results in little or no field piping, thereby overcoming some of the above-discussed disadvantages of the above systems. However, two disadvantages associated with a self-contained, refrigerated display case having a single reciprocating compressor are that the reciprocating compressor generates too much acoustic noise for the sale floor of the supermarket, and that the unit does not allow for variable capacity control. Because of the lack of variable capacity control, the compressor may perform unnecessary cycling, which may be detrimental to the stored commodity (e.g., sensitive food products) refrigerated by the merchandiser.
It would be beneficial to have another alternative to the above systems and units.